The present invention relates to a method of detecting the operating state of a friction clutch.
German Published Patent Application No. 196 52 244 describes a method of detecting the operating state of a friction clutch, which is based on a clutch arranged in the power flow between a drive motor and a gearbox and the control of the torque that can be transmitted by such a clutch during the engagement and disengagement operations. In order to control such a clutch, the entire clutch characteristics must be known, presupposing knowledge of the clutch characteristic curve. In this conventional method, the knowledge of the engagement point, referred to as the grouping point, is critical to the extent that the engagement point of a clutch characterizes the point of engagement or the engagement travel at which the transmission of torque begins. Therefore, given knowledge of the engagement point, the clutch characteristics are also substantially known. In this method, measures are taken to account for deviations between the actual physical engagement point and the stored engagement point, the deviations arising due to long-term wear phenomena and/or short-term changes in operating conditions, such as temperature changes, etc., in an adaptive manner for the control.
It is an object of the present invention to provide a method of detecting the operating state of a friction clutch for more complex torque transmission assemblies, such as torque converters, in particular step-change gearboxes which operate with friction clutches which may be engaged and disengaged axially, to permit lifetime monitoring with regard to wear, in order to perform repairs in good time and thus to avoid expensive consequential damage.
The above and other beneficial objects of the present invention are achieved by providing a method as described herein.
In the method according to the present invention, the engagement point of the clutchxe2x80x94established during the first or a subsequent actuationxe2x80x94is determined, however, during each actuation or each second actuation or each third actuation or each nth actuation, and in each case its associated engagement travel is compared with a maximum permissible value until finally, when the maximum permissible value is reached, a signal is displayed, so that repairs may be performed.
For safety reasons, it may be advantageous to use the method according to the present invention as early as in the new state of the assembly operating with at least one friction clutch, it being possible for the maximum permissible engagement travel to be predefined as the permissible differential travel and to be used for the comparison.
The method according to the present invention may be advantageous in particular in the case of synchronized step-change gearboxes. In this case, the engagement point of the new gearbox may be registered for each gear during initial commissioning, and the engagement travel relating thereto may be stored over the lifetime. Thereafter, this engagement point over its engagement travel is continuously compared with the xe2x80x9cnewxe2x80x9d value during each further gear-shift operation, and the wear travel is thus determined. If this value exceeds the stored permissible wear value, this condition is displayed by the diagnostic system and repairs are performed.
The present invention may also be advantageous with respect to monitoring the synchronization wear by changing the frictional value not being possible, since modern synchronizing systems maintain a virtually constant frictional value over their entire lifetime. A sharp change in the frictional value is only encountered in the case of complete wear of the friction lining.
In current step-change gearboxes, in which the gear-changing operations may also even be performed under automatic control, use is generally made of blocking synchronizing devices as an advance friction clutch for equalizing the rotational speed by transmitting force, which, by a blocking device, permits the gear to be engaged in a form-fitting manner only after the sychronizing operation has been completed. These blocking synchronizing devices may be constructed as single-cone, double-cone or multiple-cone synchronizing devices. The method according to the present invention may be applied to all such synchronizing devices in which wear may be detected via the clutch travel.